A latex immunoagglutination assay (latex turbidimetric immunoagglutination method) (hereinafter also referred to as an LTIA method) is frequently used in the field of clinical examination as a measurement (assay) method of an analyte (hereinafter also referred to as a target component) in a biological sample. The LTIA method is a measurement method using, for example, latex particles supporting an antibody to a target component (hereinafter also referred to as antibody-supporting latex particles) so as to detect a degree of agglutination (turbidity) of latex particles generated due to binding of an antigen, i.e., the target component, and the antibody-supporting latex particles, with an optical means (e.g., a turbidimetric method measuring transmitted light, a nephelometric method measuring scattering light) etc.
It is known that a surfactant-like substance interferes with immunological measurement systems including the LTIA method. The presence of a certain surfactant in an immunological measurement system may cause a problem such as inhibiting of an antigen-antibody reaction itself and dissociating of the antigen-antibody binding formed by the antigen-antibody reaction. The LTIA method is a homogeneous measurement method in which an antigen-antibody reaction is performed in one liquid phase, and results in an environment in which materials making up a measurement system such as the antibody-supporting latex particles are continually exposed to surfactant during measurement and, therefore, this may lead to the occurrence of interferences to the measurement system in a composite manner, such as causing a change in the structure of an analyte itself, the formation of a complex with an analyte, the nonspecific adsorption to the antibody-supporting latex particles, and the detachment of antibodies and blocking proteins supported by latex particles, due to the surfactant.
When blood is collected from a subject in the case where blood (whole blood, serum, or plasma) is used as a biological sample, preventive components (hereinafter also referred to as blood collection tube-processing agents) may have been applied to the inner wall and the cap of a blood collection tube so as to prevent blood (blood clot) from sticking to the inner wall of the blood collection tube and bubbling in the blood collection tube and the cap portion and to prevent insufficient coagulation for acquiring serum and insufficient separation of serum layer and blood cell layer. A certain kind of silicone compound is used by itself as a blood collection tube-processing agent and is used as a medium for applying other blood collection tube-processing agent than silicone compounds to the inner wall and the cap in some cases.
Some reports have been made for the interference to the LTIA method from a component applied to the inner wall of a blood collection tube. Non-Patent Literature 1 reports that a reduction in measurement value is observed when a measurement sample acquired with a commercially available micro blood collection tube is measured with the LTIA method. Non-Patent Literature 1 points out water-soluble silicone released from the inner wall of the blood collection tube as a causative substance and describes measurement results in which measurement samples with water-soluble silicone added were measured with a plurality of LTIA reagents. In Non-Patent Literature 1, consideration is also given to the interference when surfactants (BRIJ®35, TWEEN®20, TRITON® X-100) were added to measurement samples and it is reported that the reduction in measurement value was observed as was the case with water-soluble silicone. Non-Patent Literature 2 reports that measurement samples acquired with a plurality of blood collection tubes were measured with a plurality of LTIA reagents and that the reduction in measurement value was observed when a measurement sample acquired with a micro blood collection tube was measured as was the case with Non-Patent Literature 1, and water-soluble silicone released from the inner wall of the blood collection tube is also pointed out as a causative substance in this case.
A micro blood collection tube is often used when blood is collected from newborns having a smaller body weight as compared to adults. Even if the micro blood collection tube is used, a predetermined amount of blood cannot easily be collected in some cases, resulting in collected blood less than the predetermined amount. In such a case, a concentration of the blood collection tube-processing agent is increased in the measurement sample and the interference to the measurement system is expected to be prominent.
The surfactants considered in Non-Patent Literature 1 are used as nonspecific reaction-preventing agents and cleaning agents in immunological measurement methods including ELISA and are also frequently used in biochemical automated analyzers used in clinical assays as cleaning agents of: probes for dispensing or stirring measurement samples and reagents; flow passages of reagents; and repeatedly used reaction tanks. Thus, attention must be given to the interference due to mixing of the surfactants into a measurement system in the case of LTIA agents which are necessarily used in the automated analyzers.
Despite such a situation, no report has been made of a method of avoiding the interference from these surfactants and a method of reducing the interference from the surfactants when a measurement sample acquired through a micro blood collection tube is measured with the LTIA method in particular.